Understanding and characterizing tropical hydrology in Hawaii

Freshwater is a critical natural resource for Hawai’i. It sustains agriculture, tourism, urban development, and provides municipal water usage. In particular, the clean freshwater resources in Hawai’i islands depends on the health of mountain forests, which capture and absorb rain and moistures from the atmosphere. Yet Hawai’i is losing its native forest coverage to grassland and invasive vegetation, which could increase surface runoff, soil erosion, and evapotranspiration in the watersheds. The natural streamflow regime is an endpoint of a watershed, and is a realization of healthy forest ecosystem. The natural flow regime is influenced by climate, geology, and soil condition, as well as land cover and anthropogenic alteration. Yet, previously studies describe natural flow regime based on temperate forest and, therefore, it is not applicable to the flow from unique tropical forests in Hawai’i. This project proposed to understand the water resources protected by Hawai’i natural forests and strategically characterize the natural flow regime of tropical forest watersheds in Hawai’i. The goal of this project is to establish a baseline of natural flow regime from healthy forest watersheds. Its application will promote the conservation and protection of healthy forests. In particular, because flow regime dictates the sediment and nutrient regimes, the water availability to urban and agricultural usages, and influences downstream coastal ecosystems, the knowledge gained from this project would provide water resources management and for investment in restoration of the Hawaiian tropical forest. Ultimately, we would like to evaluate the possibility to address water availability upon future climate. PI: Yin-Phan Tsang

Understanding and characterizing water quality in Hawaii

Water is a critical natural resource for Hawai’i. As the water flows through the natural land units – watersheds, it carries water as well as nutrients that supply the natural and anthropogenic systems downstream. Water and nutrient budgets are important information for water resources and watershed management. However, our knowledge on instream nutrient transport and processes was established from temperate and continental systems. Little has been studied in the unique Hawaii’s watersheds. This project proposes to characterize the water availability and the nutrient transport in Hawaii’s watersheds. In specific, the current and previous effort of water quantity and quality monitoring from multiple federal and state agencies will be identified and documented. The meta information of the data will be collected to identify the gaps in our knowledge on water quantity and quality in Hawaii’s watersheds. When possible, additional survey and monitoring will be conducted at the identified watersheds. Depending on data availability, analyses and modeling studies will be performed in pilot watersheds to describe the nutrient dynamics in Hawaii’s watershed. This project aims to establish a baseline of water quantity and quality of Hawaii. Additionally, having the knowledge of nutrient loading in a watershed will be informative to regulate nutrient effluence of agriculture and urban development, and to limit the impact of the coastal environment. Its application will promote the conservation and protection of healthy watersheds in Hawaii. PI: Yin-Phan Tsang

Assessing the Impact of Future Climate on Hawai‘i’s Aquatic Ecosystems

The stream systems of Hawai‘i are unique and home to many rare species, including five native fish and five native shellfish. These native species have amphidromous life cycles, meaning that they spend part of their lives in the ocean and part in freshwater streams. Streamflow serves as a vital natural pathway, connecting saltwater and freshwater habitats so that these animals can migrate between them and carry out critical life stages (e.g., development, reproduction). Over the last 20 years, the amount of rainfall in Hawai‘i has decreased, and climate models predict that this trend will continue. It is uncertain how reduced rainfall will affect streamflow and, consequently, the native stream species that depend on it. This study will advance our understanding of what climate change means for streamflow and native stream species in Hawai‘i. Such information can be used to inform conservation management decision making. PI: Yin-Phan Tsang